Passive power sharing of paralleled sources

ABSTRACT

System and methods for passive power sharing of parallel sources are provided. Aspects include a first DC power supply including a first generator and a rectifier circuit, a second DC power supply including a second generator and a second rectifier, wherein a first output of the first DC power supply and a second output of the second DC power supply are commonly coupled at a common bus point, a first current sensing device coupled between the first output of the first DC power supply and the common bus point, a first generator controller configured to receive a first current signal from the first current sensing device, analyze the first current signal to determine a first voltage droop value based on the first current signal, and operate the first DC power supply to reduce a first voltage output of the first DC power supply by the first voltage droop value.

BACKGROUND

The present invention generally relates to parallel direct current (DC)sources, and more specifically, to passive power sharing of paralleledsources.

Aircraft require electrical power to operate many parts of the aircraftsystem, including on-board flight control systems, lighting, airconditioning etc. The current and future generations of aircraft usemore and more electrical control in place of conventional hydraulic,pneumatic etc. control. Such more electric aircraft (MEA) haveadvantages in terms of the size and weight of the controls and powersystems as well as in terms of maintenance and reliability.

Most current large commercial aircraft use electricity, on-board, in theform of an AC fixed frequency and/or variable frequency network. Stepshave been made to move from 115 V ac to 230 V ac and more recentdevelopments have allowed power supplies to supply high voltage dc(HVDC) e.g. +/−270 V dc, providing improvements in terms of additionalfunctionality, power supply simplification, weight savings and thus fuelefficiency.

Generally, voltage is provided on board an aircraft in one of two (ormore) ways. When the aircraft is on the ground, power comes from anexternal ground generator supplying, say 115 V ac at 400 Hz. Anauto-transformer rectifier unit (ATRU) rectifies the supply voltage toprovide voltages required for the different loads on the aircraft.Instead of an ATRU, the power can be rectified by active rectificationusing power flow controllers.

When the aircraft is in the air the power comes from the aircraft engineor auxiliary power unit (APU) via a three-phase ac generator that couldthen be rectified. The rectified power is provided to a so-called DCbus.

BRIEF DESCRIPTION

Embodiments of the present invention are directed to a system. Anon-limiting example of the system includes a first direct current (DC)power supply including a first generator and a first rectifier circuit,a second DC power supply including a second generator and a secondrectifier, wherein a first output of the first DC power supply and asecond output of the second DC power supply are commonly coupled at acommon bus point, a first current sensing device coupled between thefirst output of the first DC power supply and the common bus point, afirst generator controller configured to receive a first current signalfrom the first current sensing device, analyze the first current signalto determine a first voltage droop value based on the first currentsignal, and operate the first DC power supply to reduce a first voltageoutput of the first DC power supply by the first voltage droop value.

Embodiments of the present invention are directed to a method. Anon-limiting example of the method includes providing a first directcurrent (DC) power supply including a first generator and a firstrectifier circuit, providing a second DC power supply including a secondgenerator and a second rectifier, wherein a first output of the first DCpower supply and a second output of the second DC power supply arecommonly coupled at a common bus point, providing a first currentsensing device coupled between the first output of the first DC powersupply and the common bus point, receiving, by a first generatorcontroller, a first current signal from the first current sensingdevice, analyzing, by the first generator controller, the first currentsignal to determine a first voltage droop value based on the firstcurrent signal, and operating, by the first generator controller, thefirst DC power supply to reduce a first voltage output of the first DCpower supply by the first voltage droop value.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a perspective view of an aircraft that may incorporateembodiments of the present disclosure;

FIG. 2 depicts a block diagram of a passive power sharing system withtwo parallel sources according to one or more embodiments;

FIG. 3 depicts a block diagram of a generator controller performingdroop control for a generator according to one or more embodiments; and

FIG. 4 depicts a flow diagram of a method for passive power sharing ofparallel sources according to one or more embodiments.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related to making andusing aspects of the invention may or may not be described in detailherein. In particular, various aspects of aircraft electric powersystems to implement the various technical features described herein arewell known. Accordingly, in the interest of brevity, many conventionalimplementation details are only mentioned briefly herein or are omittedentirely without providing the well-known system and/or process details.

FIG. 1 illustrates an example of a commercial aircraft 10 havingaircraft engines 20 that may embody aspects of the teachings of thisdisclosure. The aircraft 10 includes two wings 22 that each include oneor more slats 24 and one or more flaps 26. The aircraft further includesailerons 27, spoilers 28, horizontal stabilizer trim tabs 29, rudder 30and horizontal stabilizer 31. The term “control surface” used hereinincludes but is not limited to either a slat or a flap or any of theabove described. It will be understood that the slats 24 and/or theflaps 26 can include one or more slat/flap panels that move together.The aircraft 10 also includes a system 200 (described in greater detailin FIG. 2) which allows for passive power sharing for parallel sourcesaccording to one or more embodiments. The parallel sources can supplypower to a DC bus that provides power for a variety of powerapplications on the aircraft.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the disclosure, when the aircraft is in the airthe power comes from an electric power generating system (EPGS) whichtypically includes one or more generators. An example generatorincludes, but is not limited to, permanent magnet generators (PMG) thatinclude permanent magnets mounted on a rotating shaft driven by a primemover such as the turbine engine on the aircraft. The power generatorfrom these generators can be rectified to provide a DC power supply topower a DC bus on the aircraft. In some instances, it may be desirableto have two (or more) DC power supplies operating in parallel to provideDC power to the DC bus. This allows for the DC power bus to provide morepower for large loads such as an electrical propulsion system.

Using parallel DC power supplies provide flexibility when there is ademand for a high load current that is more than a single DC powersupply can provide. Advantages of the parallel supplies versus using alarger DC power supply includes the ability for independent channeloperation, installation flexibility & the load management configuration.

However, two or more DC power supplies connected in parallel do notautomatically share a load equally. Even if the power supplies areidentical, the output voltages will be slightly different due tocomponent tolerances and a variety of other factors. The power supplywith the higher voltage output will typically provide the entire loadcurrent, operating at its limit while the other power supply essentiallydoes very little work. This scenario is not optimal because itessentially overloads a power supply which could cause the power supplyto fail at a faster rate.

In one or more embodiments, aspects described herein address powersharing amongst parallel DC power supplies by providing a passive powersharing system and associated methodology for operation. This passivepower sharing includes reducing the DC voltage output of an individualDC power source as a function of its load current. This enables socalled passive power sharing whereby only load information of the sourceitself is used to adjust its voltage output. Conversely, “active” loadmanagement takes into account the entire system load (i.e., summed loadof the other sources) to regulate the load sharing as a portion of thesystem load. Advantages of this passive load sharing architecture isthat less system communication is required making it more robust,allowing the system to continue to operate in the event system loadinformation is lost.

FIG. 2 depicts a block diagram of a passive power sharing system withtwo parallel sources according to one or more embodiments. The system200 includes two generators 204 a, 204 b. In one or more embodiments,the generators 204 can be a permanent magnet generator (PMG) on anaircraft as discussed above. The system 200 also includes a tworectifiers 206 a, 206 b which can be any type of rectifier circuitincluding both active and passive rectifiers. The system 200 includes animpedance 208 a, 208 b to capture parasitic impedance of the feeders. Ingeneral, the bus includes feeder impedances (e.g. resistance andinductance between the generator and rectifier, as part of therectifier/filter circuit, between the rectifier and point of commoncoupling (PCC), and between the PCC and the load. As shown in the system200, the DC bus is commonly coupled to provide DC power to the load 220at a point of common coupling. The DC bus can have a filter 210 attachedprior to the commonly coupled DC bus providing power to the load 220. Insome embodiments, the filter 210 can be positioned before the point ofcommon coupling of the DC bus, for example two filters could be directlyafter the two rectifiers 206 a, 206 b. The filter 210 can be any type ofelectronic filter.

In one or more embodiments, the generators 204 a, 204 b are controlledand operated by a generator controller 202 a, 202 b. Further, thegenerator controllers 202 a, 202 b are configured to receive currentreadings and/or signals from a current sensing device 212 a, 212 bbefore the point of common coupling of the sources. The current sensingdevices 212 a, 212 b can be any type of device operable to sense currentvalues from a bus such as, for example, a hall effect sensor or acurrent sense resistor.

In one or more embodiments, the generator controllers 202 a, 202 b areconfigured to reduce or “droop” the voltage output of the generators 204a, 204 b in the system 200 responsive to sensing a feedback currentmeasured from the current sensing devices 212 a, 212 b. Each generatorcontroller 202 a, 202 b performs this drooping of the voltage for theirrespective generator 204 a, 204 b independent of the current valuemeasured for the other generator and independent of the current of theentire system load 220. For example, generator 204 a produces an ACvoltage that is rectified by the rectifier circuit 206 a to produce a DVvoltage to the DC bus. Prior to the point of the common coupling of theDC bus, the DC current is measured by current sensing device 212 a andprovided to the generator controller 202 a. The generator controller 202a analyzes this DC current and provides a command to droop the voltageof the generator 204 a based on this DC current value. In one or moreembodiments, the command to droop the voltage of a generator 204 a, 204b can be calculated, for example, as a function of the DC current value.

FIG. 3 depicts a block diagram of a generator controller 202 performingdroop control for a generator according to one or more embodiments. Thecontroller 202 receives the DC current feedback from the current sensingdevice 212 which is passed through a low pass filter 302. The low passfilter 302 can be any type of low pass filter circuit design. The lowpass filter 302 filters out noise that may be present in the DC currentfeedback from the current sensing device 212. The controller 202includes a droop control 304 module that includes a max voltage drooplimit 306. The max voltage droop 306 can be pre-programmed to cap thevoltage does not droop by a maximum amount, for example, 5V. In one ormore embodiments, the droop control 304 module can calculate the voltagedroop utilizing two methodologies. The first methodology is using afunction calculation 308 where a mathematical function is defined andthe current feedback value is inputted to determine a droop voltage. Forexample, a simplified function defined as drooping the voltage by 3 Vfor every 100 amps sensed can be used. In this instance, the currentvalue is multiplied times 3/100 to determine the voltage droop. Forexample, a 150 amp current feedback value would produce a voltage droopvalue of 4.5V (150*3/100). In another example, a 200 amp currentfeedback value would produce a voltage droop value of 5V. This 5V wouldbe the max voltage droop defined since the function would have produced6V (200*3/100). This function calculation for the voltage droop isexemplary. Any type of function calculation can be utilized for droopcontrol including any linear or non-linear function using the currentfeedback value. In one or more embodiments, a lookup table 310 can beutilized for calculating the voltage droop value by the droop control304 module. The lookup table 310 can include stored voltage droop valueswith corresponding current feedback values. The drop control 304 modulecan determine the current feedback value and select the voltage droopvalue based on these values in the lookup table 310.

In one or more embodiments, either the function calculation 308 orlookup table 310 can be utilized by the droop control 304 module todetermine the droop voltage value for the generator controller 202. Thegenerator controller 202 can operate the generator 204 (from FIG. 2) toreduce its output voltage by the calculated droop voltage value. Forexample, in a wound field synchronous machine, the generator controllerwould adjust the field current in order lower the output voltage. In thecase of a PMG, a power converter can be included to lower the DC linkvoltage (e.g. an active rectifier). Another example for adjusting PMGoutput voltage includes adjusting the speed of the generator, ifavailable as an option in the generator configuration. In one or moreembodiments, the generator controllers 202 a, 202 b can receive DCcurrent values from the current sensing devices 212 a, 212 b at adefined sampling rate. An exemplary sampling rate could be between50-100 μs. Any sampling rate can be utilized herein.

In one or more embodiments, the generator controller 202 a, 202 b or anyof the hardware referenced in the system 200 can be implemented byexecutable instructions and/or circuitry such as a processing circuitand memory. The processing circuit can be embodied in any type ofcentral processing unit (CPU), including a microprocessor, a digitalsignal processor (DSP), a microcontroller, an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), orthe like. Also, in embodiments, the memory may include random accessmemory (RAM), read only memory (ROM), or other electronic, optical,magnetic, or any other computer readable medium onto which is storeddata and algorithms as executable instructions in a non-transitory form.

FIG. 4 depicts a flow diagram of a method for passive power sharing ofparallel sources according to one or more embodiments. The method 400includes providing a first direct current (DC) power supply comprising afirst generator and a first rectifier circuit, as shown in block 402. Atblock 404, the method 400 includes providing a second DC power supplycomprising a second generator and a second rectifier, wherein a firstoutput of the first DC power supply and a second output of the second DCpower supply are commonly coupled at a common bus point. The first DCpower supply and the second DC power supply can be arranged as parallelpower supplies to provide high voltage DC current to a DC bus on anaircraft for various applications. The method 400 also includesproviding a first current sensing device coupled between the firstoutput of the first DC power supply and the common bus point, as shownin block 406. At block 408, the method 400 includes receiving, by afirst generator controller, a first current signal from the firstcurrent sensing device. The method 400 then includes analyzing, by thefirst generator controller, the first current signal to determine afirst voltage droop value based on the first current signal, as shown inblock 410. And at block 412, the method 400 includes operating, by thefirst generator controller, the first DC power supply to reduce a firstvoltage output of the first DC power supply by the first voltage droopvalue.

Additional processes may also be included. It should be understood thatthe processes depicted in FIG. 4 represent illustrations, and that otherprocesses may be added or existing processes may be removed, modified,or rearranged without departing from the scope and spirit of the presentdisclosure.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

Various embodiments of the invention are described herein with referenceto the related drawings. Alternative embodiments of the invention can bedevised without departing from the scope of this invention. Variousconnections and positional relationships (e.g., over, below, adjacent,etc.) are set forth between elements in the following description and inthe drawings. These connections and/or positional relationships, unlessspecified otherwise, can be direct or indirect, and the presentinvention is not intended to be limiting in this respect. Accordingly, acoupling of entities can refer to either a direct or an indirectcoupling, and a positional relationship between entities can be a director indirect positional relationship. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” may be understood to include any integer numbergreater than or equal to one, i.e. one, two, three, four, etc. The terms“a plurality” may be understood to include any integer number greaterthan or equal to two, i.e. two, three, four, five, etc. The term“connection” may include both an indirect “connection” and a direct“connection.”

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A system comprising: a first direct current (DC)power supply comprising a first generator and a first rectifier circuit;a second DC power supply comprising a second generator and a secondrectifier, wherein a first output of the first DC power supply and asecond output of the second DC power supply are commonly coupled at acommon bus point; a first current sensing device coupled between thefirst output of the first DC power supply and the common bus point; afirst generator controller configured to: receive a first current signalfrom the first current sensing device; analyze the first current signalto determine a first voltage droop value based on the first currentsignal; and operate the first DC power supply to reduce a first voltageoutput of the first DC power supply by the first voltage droop value. 2.The system of claim 1, wherein the first DC power supply is in parallelwith the second DC power supply.
 3. The system of claim 1, furthercomprising: a second current sensing device coupled between a secondoutput of the second DC power supply and the common bus point; and asecond generator controller configured to: receive a second currentsignal sensed from the second current sensing device; analyze the secondcurrent signal to determine a second voltage droop value based on thesecond current signal; and operate the second DC power supply to reducea second voltage output of the second DC power supply by the secondvoltage droop value.
 4. The system of claim 1, wherein the determiningthe first voltage droop value comprises: filtering, by an electronicfilter, the first current signal; determining a voltage droop function;and inputting the first current value into the voltage droop function todetermine the first voltage droop value.
 5. The system of claim 4,wherein determining the first voltage droop value further comprising:determining, by the first generator controller, a maximum voltage droopvalue; comparing the first voltage droop value to the maximum voltagedroop value; and setting the first voltage droop value to the maximumvoltage droop value based on a determination that the first voltagedroop value exceeds the maximum voltage droop value.
 6. The system ofclaim 4, wherein the voltage droop function comprises a linear function.7. The system of claim 1, wherein the determining the first voltagedroop value comprises: filtering, by an electronic filter, the firstcurrent signal; determining a lookup table comprising a set of voltagedroop values; and comparing the first current signal to the set ofvoltage droop values in the lookup table to determine the first voltagedroop value.
 8. The system of claim 7, wherein determining the firstvoltage droop value further comprising: determining, by the firstgenerator controller, a maximum voltage droop value; comparing the firstvoltage droop value to the maximum voltage droop value; and setting thefirst voltage droop value to the maximum voltage droop value based on adetermination that the first voltage droop value exceeds the maximumvoltage droop value
 9. The system of claim 1, wherein the first currentsensing device comprises a hall effect sensor.
 10. The system of claim1, wherein the first generator comprises a wound field synchronousgenerator.
 11. A method comprising: providing a first direct current(DC) power supply comprising a first generator and a first rectifiercircuit; providing a second DC power supply comprising a secondgenerator and a second rectifier, wherein a first output of the first DCpower supply and a second output of the second DC power supply arecommonly coupled at a common bus point; providing a first currentsensing device coupled between the first output of the first DC powersupply and the common bus point; receiving, by a first generatorcontroller, a first current signal from the first current sensingdevice; analyzing, by the first generator controller, the first currentsignal to determine a first voltage droop value based on the firstcurrent signal; and operating, by the first generator controller, thefirst DC power supply to reduce a first voltage output of the first DCpower supply by the first voltage droop value.
 12. The method of claim11, wherein the first DC power supply is in parallel with the second DCpower supply.
 13. The method of claim 11, further comprising: providinga second current sensing device coupled between a second output of thesecond DC power supply and the common bus point; and receiving, by asecond generator controller, a second current signal sensed from thesecond current sensing device; analyzing, by a second generatorcontroller, the second current signal to determine a first voltage droopvalue based on the second current signal; and operating, by a secondgenerator controller, the second DC power supply to reduce a secondvoltage output of the second DC power supply by the second voltage droopvalue.
 14. The method of claim 11, wherein the determining the firstvoltage droop value comprises: filtering, by an electronic filter, thefirst current signal; determining a voltage droop function; andinputting the first current value into the voltage droop function todetermine the first voltage droop value.
 15. The method of claim 14,wherein determining the first voltage droop value further comprising:determining, by the first generator controller, a maximum voltage droopvalue; comparing the first voltage droop value to the maximum voltagedroop value; and setting the first voltage droop value to the maximumvoltage droop value based on a determination that the first voltagedroop value exceeds the maximum voltage droop value.
 16. The method ofclaim 14, wherein the voltage droop function comprises a linearfunction.
 17. The method of claim 11, wherein the determining the firstvoltage droop value comprises: filtering, by an electronic filter, thefirst current signal; determining a lookup table comprising a set ofvoltage droop values; and comparing the first current signal to the setof voltage droop values in the lookup table to determine the firstvoltage droop value.
 18. The method of claim 17, wherein determining thefirst voltage droop value further comprising: determining, by the firstgenerator controller, a maximum voltage droop value; comparing the firstvoltage droop value to the maximum voltage droop value; and setting thefirst voltage droop value to the maximum voltage droop value based on adetermination that the first voltage droop value exceeds the maximumvoltage droop value
 19. The method of claim 11, wherein the firstcurrent sensing device comprises a hall effect sensor.
 20. The method ofclaim 11, wherein the first generator comprises a wound fieldsynchronous generator.